This work used K-means (k=3) after PCA analysis on 109 PDO Maine-Anjou cows according to the abundances of small and large heat shock proteins (HSPs) in the Longissimus thoracis muscle. Classes LP (n=24) and SP (n=33) were characterized by greater abundances of large and small HSPs, respectively, while class IP (n=52) was intermediate. The classes were compared for the abundance of other proteins in the same muscle and for meat tenderness. The effects of pre-slaughter factors (transport and lairage durations) were also investigated. Meat tenderness did not differ for any comparison. Certain proteins were influenced by pre-slaughter conditions. Among them, H2AFX and µ-calpain were impacted by both factors. The possible role of H2AFX (H2A histone family, member) in the balance of various processes involved in meat tenderization is discussed.